In the related art, the structure of an air flow control valve with a plurality of valve main body portions that are respectively provided in each of a plurality of intake ports, and control the flow of a fluid supplied to a combustion chamber of an internal combustion engine has been known (for example, refer to EP-1388652 (Reference 1)).
EP-1388652 (Reference 1) discloses the structure of the valve (the structure of the air flow control valve) for opening and closing each of the intake ports in an intake manifold (intake device) with the plurality of intake ports. In the structure of the valve disclosed in EP-1388652 (Reference 1), the plurality of intake ports are respectively provided with a plurality of flaps (valve main body portions), each of which has a curved shape and is disposed so as to be turnable in the intake port, and a plurality of shafts (turning shafts (connecting shafts)), each of which connects the adjacent flaps. Each of the shafts is turnably supported by a bearing structure formed in a wall portion of the intake port. In the configuration of the intake port, an inner circumferential surface (bearing surface) is formed in a bearing portion formed of bearing member pieces which are assembled in such a manner that two pre-split bearing member pieces face each other and the shaft is interposed between the bearing member pieces.
In the structure of the valve (the structure of the air flow control valve) in the intake manifold (intake device) disclosed in EP-1388652 (Reference 1), since the inner circumferential surface (bearing surface) is formed in the bearing portion formed of the bearing member pieces which are assembled in such a manner that the two split bearing member pieces face each other and the shaft is interposed between the bearing member pieces, it is necessary to set a clearance (gap) between an outer surface of the shaft (connecting shaft) and the bearing surface (inner surface) of the bearing portion formed of the bearing member pieces, while taking into consideration an assembly error (a relative positional offset between the bearing member pieces originating from the assembly of the bearing member pieces).
That is, it is necessary to set the clearance (the clearance between the outer surface of the shaft and the bearing surface of the bearing member pieces) to be slightly large so that a given gap is ensured even when the relative positional offset occurs between the bearing member pieces. When the clearance is set to be slightly large, and the shaft turns in a state where an offset (step) is formed between the mating surfaces (the bearing surface) of the bearing member pieces facing each other, the shaft is brought into local contact (partial contact phenomenon) with the bearing surface due to the shape of the step between the bearing surfaces (mating surfaces), and the bearing surface is subjected to wear. When the bearing member pieces are assembled without an occurrence of an assembly error, the gap between the outer surface of the shaft and the bearing surface of the bearing portion increases due to the setting of the clearance (the clearance between the shaft and the bearing portion) to be slightly large, and as a result, backlash of the shaft increases. There is a problem in that when the bearing portion is formed by assembling together a plurality of (two) split bearing member pieces, the bearing surfaces may be subjected to wear due to the stepped shape of the bearing surfaces originating from the assembly error, or the backlash of the shaft (connecting shaft) may increase due to an excessive clearance.